1. Field of Technology
The present disclosure relates to cutting tools, cutting inserts, and techniques for machining metals and metallic alloys. The present disclosure more specifically relates to slotting cutters and cutting inserts adapted for use with such cutters, and to techniques for machining metals and alloys using such cutting tools.
2. Description of the Background of the Technology
Slotting cutters are used in the metal working industry to machine full or partial slots in a part piece. A typical slotting cutter comprises a circular cutter body, and one or more high speed steel (“HSS”), carbide, or ceramic cutting inserts. These inserts are positioned around the periphery of the cutter body. The slotting cutter is attached to a machine spindle and rotated at speeds sufficient to remove material from a part piece when contact is made between the inserts and the part piece. Slotting cutters can be right hand, left hand or neutral, depending upon the axial location of the inserts on the cutter body.
A major concern in the cutting tool industry is retention of cutting inserts on the cutter body. The inserts must be securely and accurately fastened to the cutting tool body and also must be able to be quickly installed and replaced. Secure and accurate attachment is especially important when ceramic inserts are used because cutting speeds in excess of 1000 surface feet per minute (“SFM”) are common and any slight insert movement or inaccuracy in the location of the inserts in designs where multiple inserts are used can result in catastrophic failure. These inserts must be fully retained both axially and radially.
Another major concern in the cutting tool and machining industry is the availability of machine time. Increased production may have a positive financial impact on production facilities. Personnel working in the industry are continually looking for ways to improve machine throughput and thus improvements in machine production. These solutions can be accomplished in a number of ways including improving performance on a particular machine or switching production to a more efficient machine from a less efficient machine.
Parts such as turbine disks typically have been machined using a technique known as broaching. Turbine disks are often found in various turbine assemblies. Multiple turbine disks are located along the length of a turbine shaft and are used to connect the turbine blades to the turbine shaft. A typical slot machined in the turbine disk corresponds to the shape of the end of a turbine blade. The turbine blade may then be fit into the slot of the turbine disk thus securing the turbine blade to the turbine disk. These turbine blades cause the turbine shaft to rotate when a gas or liquid is passed over the blades.
The slot formed in the turbine disk is normally machined using a broaching technique. Broaching is a type of machining where a cutting tool with a number of progressively increasing cutting edges is pushed or pulled over a machine surface to make a cut. For example, in turbine disk manufacturing, a “Christmas tree” or “fir tree” shaped keyway must be cut on the periphery of the turbine disk to accept a corresponding shaped end of a turbine blade. These keyways have been typically cut using broaching with a cutting tool that has progressively larger “fir trees” as the cut is made. Broaching is an extremely slow and costly method of machining. The broaches used to machine turbine disks typically include broach segments to rough and finish a slot. Other techniques have been attempted including grinding and wire electronic discharge machine (“EDM”). The use of a slotting cutter may provide a faster and more efficient method of machining rough slots on a turbine disk. Subsequent to machining the rough slots, the disk may be further machined to provide each of the slots with the shape required in the finished turbine component. This shape may be quite complex. Although finish machining may require the use of broaching, the rough slot is machined much more quickly, and potentially more cost effective, given the increased production of a slotting cutter versus a broaching machine.
Turbine disks are conventionally formed of nickel-based superalloys, such as Alloy 718 (UNS N017718) and Rene 95™ alloy. These nickel-based superalloys are often referred to as high temperature alloys. Nickel-based superalloys are very difficult to machine due to their hardness and abrasiveness, among other things. Metals are given a machinability rating which indicates the difficulty of machining that metal. A metal with a high machinability rating is much easier to machine than a metal with a lower machinability rating. Generally, the machinability rating of a nickel-based superalloy is approximately 10% of the machinability rating of cold-rolled steel. Broaching has typically been required to machine these alloys. Manufacturers of turbine disks have been looking for a method to machine turbine disks more quickly. What is needed is a less costly and more efficient method for machining turbine disks.